1. Field of the Invention
The present invention relates to an electronic sphygmomanometer and a measuring method for blood pressure and pulse using the electronic sphygmomanometer, and particularly relates to a measuring device for measuring blood pressure and pulse by using a cuff and a method thereof.
2. Description of the Related Art
In the past, sphygmomanometers in which a cuff (air bladder) is mounted on a measurement location such as a wrist or an upper arm, and blood pressure is calculated from cuff pressure fluctuation that is transmitted from an artery, have become popular. As the sphygmomanometer used for measuring the blood pressure variation for an extended period of time, the wrist sphygmomanometer in which a cuff is mounted on the wrist may reduce the burden on a patient compared to that in which the cuff is mounted on an upper arm. It could be said that the radial artery at the wrist is a better suited location for measuring the pulse because the artery is at a shallower location under the skin than the upper arm.
Therefore, a wrist sphygmomanometer may be a device for measuring blood pressure and pulse rate for an extended period of time.
As a measuring method for pulse, a method in which a volume change of an artery located in a comparatively shallow area under the skin is detected noninvasively to measure the pulse rate has been known. As a typical measuring method for the pulse rate, there is a method to measure the artery volume change by using a sensor, such as a photoelectronic sensor, an impedance sensor, or the like, that is arranged directly above and pressed against the artery in order to detect the volume of the artery.
In order to press the sensor to the skin to detect artery volume, a cuff used for measuring blood pressure can be used. When measuring the blood pressure by increasing and decreasing the pressure in the cuff, a pulse wave (pressure pulse wave) can be detected by the pressure sensor from the pressure variation that is superimposed on the air bladder of the cuff at that time.
FIGS. 1 (A) to (C) are drawings illustrating positional relationships of a sensor that detects an artery volume and a cuff. In other words, FIG. 1 (A) illustrates a case where the sensor that detects the artery volume is arranged at a downstream side of the artery compared to the compressed area by the cuff, FIG. 1 (B) illustrates a case where the sensor that detects the artery volume is arranged roughly in the center of the compressed area by the cuff, and FIG. 1 (C) illustrates a case where the sensor that detects the artery volume is arranged at an upstream side of the artery compared to the cuff compressed area.
FIG. 2 to FIG. 4 are graphs illustrating a relationship between a change in pulse amplitude associated with a change in the inner pressure of the cuff and a measurement result of a pattern of a pulse wave measured by a sensor that detects the artery volume arranged in each location illustrated in FIG. 1. In each graph, (A) illustrates a change of a pattern of the pulse wave associated with a change of an internal pressure of the cuff, (B) illustrates a measurement result of a pattern of the pulse wave measured by the sensor that detects the volume of the artery. Further, FIGS. 5 (A) and (B) are drawings illustrating a state of the sensor that detects the volume of the artery when compressing the cuff.
When the sensor that detects the volume of the artery is arranged at a downstream side of the artery compared to the compressed area by the cuff as illustrated in FIG. 1 (A), the pulse is no longer detected due to compression and closing of the artery by the cuff. Further, as illustrated in FIG. 5 (A), the positional relationship between the artery and the sensor that detects the volume of the artery changes in proportion to inflation of the cuff by the compression. Accordingly, as illustrated in FIG. 2, a change in the volume of the artery detected by the sensor that detects the volume of the artery is smaller in proportion to the progression of the compression and closing of the artery, and when the artery is compressed and closed, the change in volume of the artery is no longer detected.
When the sensor that detects the volume of the artery is arranged roughly in the center of the compressed area by the cuff as illustrated in FIG. 1 (B), as similar to the case in FIG. 1 (A), the pulse is no longer detected when the cuff compresses and closes the artery. Further, the change in the volume of the artery is gradually larger in proportion to the inflation of the cuff by compression due to the dynamic characteristics of the artery in this arrangement, and after the maximum value is exceeded, it gradually reduces, and when the artery is compressed and closed, the change in the volume of the artery is no longer detected.
When the sensor that detects artery volume is arranged in the upstream side of the artery compared to the cuff compression area as illustrated in FIG. 1 (C), the orientation of the sensor to the measurement location to detect the volume of the artery changes due to the compression by the cuff. In other words, as illustrated in FIG. 5 (B), the propositional relationship between the artery and the sensor that detects the volume of the artery changes in proportion to inflation of the cuff by compression. Therefore, the amplitude of the pulse wave detected is reduced by the compression by the cuff.
To be more precise, as is evident from the measurements, when the sensor that detects the volume of the artery is configured so as to press against the measurement location by using the cuff used for measuring blood pressure, the amplitude of the pulse wave detected by the compression of the cuff changes and the measurement cannot be carried out accurately even by arranging the sensor that detects artery volume in any positional relationship.